SUBSEQUENT EVENTS (Details) - USD ($)							2 Months Ended	3 Months Ended				12 Months Ended
	Jan. 21, 2016	Dec. 10, 2015	Sep. 10, 2015	Jun. 15, 2015	Apr. 06, 2015	Dec. 17, 2014	Mar. 04, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 26, 2016	Aug. 01, 2014	Jan. 24, 2013	Sep. 19, 2012
Subsequent Event [Line Items]
Dividends declared, not paid												$ 57,390,000
Dividends per share of common stock (in dollars per share)								$ 1.45	$ 0.275	$ 0.25	$ 0.25
Gains (losses) on extinguishment of debt												$ 0	$ (150,000)	$ 0
Percent of FHLB advances to total debt obligations outstanding								43.40%				43.40%
Revolving Credit Facility
Subsequent Event [Line Items]
Maximum amount on revolving credit line credit facility																	$ 50,000,000
Revolving Credit Facility | Subsequent Event
Subsequent Event [Line Items]
Maximum amount on revolving credit line credit facility															$ 143,000,000
Class A common stock
Subsequent Event [Line Items]
Dividends per share of common stock (in dollars per share)		$ 1.45	$ 0.275	$ 0.25	$ 0.25							$ 2.225	$ 0
Class A common stock | Subsequent Event
Subsequent Event [Line Items]
Dividends declared, not paid	$ 15,500,000
Accrued dividends payable unvested restricted stock	$ 500,000
Common stock issued as dividends (in shares)	5,607,762
Common stock equivalent dividends paid	$ 64,100,000
Common stock, dividends, weighted average price per share	$ 11.43
Common stocks dividends, trading days after election	3 days
Common stocks repurchased (in shares)							151,588
Common stock repurchased							$ 1,600,000
Common stocks repurchased (in dollars per share)							$ 10.57
Class B common stock | Subsequent Event
Subsequent Event [Line Items]
Common stock issued as dividends (in shares)	4,468,031
Series REIT LP Units | Subsequent Event
Subsequent Event [Line Items]
Common stock issued as dividends (in shares)	10,075,793
Senior Notes Due, 2017 | Senior Unsecured Notes
Subsequent Event [Line Items]
Debt instrument, repurchased face amount						$ 5,445,000
Debt instrument, repurchase price amount						5,600,000
Gains (losses) on extinguishment of debt						(200,000)
Senior Notes Due, 2017 | Senior Unsecured Notes | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, repurchased face amount							$ 20,634,000
Debt instrument, repurchase price amount							20,200,000
Gains (losses) on extinguishment of debt							200,000
Unamortized debt issuance costs							(200,000)
Senior Notes Due 2021 | Senior Unsecured Notes | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, repurchased face amount							21,700,000
Debt instrument, repurchase price amount							17,900,000
Gains (losses) on extinguishment of debt							3,500,000
Unamortized debt issuance costs							(300,000)
Senior Notes Due, 2017 | Senior Unsecured Notes
Subsequent Event [Line Items]
Debt instrument, aggregate amount						$ 319,555,000												$ 325,000,000
Senior Notes Due, 2017 | Senior Unsecured Notes | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, aggregate amount							298,921,000
Senior Notes Due 2021 | Senior Unsecured Notes
Subsequent Event [Line Items]
Debt instrument, aggregate amount																$ 300,000,000
Senior Notes Due 2021 | Senior Unsecured Notes | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, aggregate amount							278,300,000
2014 Share Repurchase Authorization Program
Subsequent Event [Line Items]
Remaining amount of stock repurchase								$ 49,000,000				$ 49,000,000
2014 Share Repurchase Authorization Program | Class A common stock
Subsequent Event [Line Items]
Remaining amount of stock repurchase								$ 49,006,000				$ 49,006,000	$ 50,000,000
2014 Share Repurchase Authorization Program | Class A common stock | Subsequent Event
Subsequent Event [Line Items]
Remaining amount of stock repurchase							$ 47,400,000